Salts of alkyl sulfonic acids are used as detergents especially in dishwashing formulations. These detergents are generally referred to as paraffin sulfonates. They can be made from so called detergent range olefins by reacting the olefin with hydrogen sulfide to form an alkyl mercaptan and then oxidizing the mercaptan to a sulfonic acid. It has been reported that this oxidation can be conducted using oxidizing agents such as nitric acid, hydrogen peroxide, chlorine plus oxygen and by oxygen in the presence of base. The present invention is concerned with this later process.
Wallace and Schriesheim have published a number of papers on their work on the base catalyzed oxidation of mercaptans. In J. Org. Chem. 27, 1514 (1962) they report the oxidation of n-butyl mercaptan at 23.5.degree. C. in methanol, tetrahydrofuran, dioxane, diglyme, dimethylacetamide, dimethylformamide, ethanol and tert-butyl alcohol. They used 2 moles of base per mole of mercaptan. The products made were disulfides, not sulfonates.
In Tetrahedron 21, 2271 (1965), Wallace et al. report the formation of sulfonic acids by increasing the amount of base to 4 moles per mole of mercaptan. Solvents used were hexamethylphosphoramide, dimethylformamide, tetramethylurea and pyridine. In methanol at a 2:1 base:mercaptan ratio only disulfides formed.
Wallace et al., J. Appl. Chem. 17, 48 (1967) report continued research using hexamethylphosphoramide, their preferred solvent, dimethylformamide, tetramethylurea, pyridine and methanol. Using methanol at 4 moles of base per mole of mercaptan only disulfides formed.
In J. Inst. Petro. 53, No. 522, 207 (1967), Wallace et al. report their research on the oxidation of mercaptans in petroleum fractions with air and an aqueous base. Normally this process is only effective up to C.sub.5 mercaptans due to the lack of solubility of the higher mercaptans in aqueous base. Solubilizers that have been used are methanol, amino alcohols, glycols, polyglycols and surfactants. Wallace et al. directed their efforts at the effect of methanol, tert-butyl alcohol, dimethoxyethane, dimethyl sulfoxide, dimethylformamide and hexamethylphosphoramide as co-solvents and found hexamethylphosphoramide to be superior. The oxidation products are disulfides. They also speculate that the mercaptide ion is the active species that is oxidized to disulfide which is why an excess of base was required.